On Mon, Sep 13, 2021 at 02:47:56PM -0500, Bjorn Helgaas wrote:
> On Sat, Sep 11, 2021 at 12:13:33PM +0200, Greg Kroah-Hartman wrote:
> > On Fri, Sep 10, 2021 at 07:21:01PM +0200, Krzysztof Wilczyński wrote:
> > > Hi Greg,
> > >
> > > [...]
> > > > > pci_dev_config_attr_is_visible(..., struct bin_attribute *a, ...)
> > > > > {
> > > > > a->size = PCI_CFG_SPACE_SIZE; # <-- set size in global attr
> > > > > ...
> > > > > }
> > > > >
> > > > > static struct bin_attribute *pci_dev_config_attrs[] = {
> > > > > &bin_attr_config, NULL,
> > > > > };
> > > > > static const struct attribute_group pci_dev_config_attr_group = {
> > > > > .bin_attrs = pci_dev_config_attrs,
> > > > > .is_bin_visible = pci_dev_config_attr_is_visible,
> > > > > };
> > > > >
> > > > > pci_device_add
> > > > > device_add
> > > > > device_add_attrs
> > > > > device_add_groups
> > > > > sysfs_create_groups
> > > > > internal_create_groups
> > > > > internal_create_group
> > > > > create_files
> > > > > grp->is_bin_visible()
> > > > > sysfs_add_file_mode_ns
> > > > > size = battr->size # <-- copy size from attr
> > > > > __kernfs_create_file(..., size, ...)
> > > > > kernfs_new_node
> > > > > __kernfs_new_node
> > > > >
> > > >
> > > > You can create a dynamic attribute and register that. I think some
> > > > drivers/busses do that today to handle this type of thing.
> > >
> > > Some static attributes users don't set size today or simply set it to 0, so
> > > then we report 0 bytes in userspace for each such attribute via the backing
> > > i-node.
> > >
> > > Would you be open to the idea of adding a .size() callback so that static
> > > attributes users could set size using more proper channels, or do you think
> > > leaving it being set to 0 is fine?
> >
> > I think leaving it at 0 is fine, are userspace tools really needing to
> > know the size ahead of time for sysfs files? What would changing this
> > help out with?
>
> We currently set the inode size for BARs (resource0, resource1, etc)
> to the BAR size. I don't think lspci uses that inode size; it looks
> at the addresses in "resource" and computes the size from that [1].
>
> But I doubt we can set the "resourceN" sizes to 0, since somebody else
> might be using that information.
>
> I'm curious to know what other static attribute users set .size.
> Maybe they're all singleton cases, as opposed to the per-device cases
> we're interested in.
Most are singleton cases from what I have seen. Or they just leave the
file size at 0. There are not that many binary sysfs files around,
thankfully.
thanks,
greg k-h
